1. Field of the Invention
The present invention relates to a thermal printer for printing an image by placing an ink ribbon and paper between a thermal head and a platen and transferring the inks of the ink ribbon onto the paper. The invention also relates to a method of forming an image using the thermal printer. More particularly, the invention relates to a technique for producing vivid visual effects by forming sufficient convexes and concaves on the surface of the paper.
2. Description of the Related Art
A thermal printer having a thermal head including arrays of plural heat-generating elements (such as heat-generating resistors) and a platen (e.g., a platen roller) mounted opposite to the thermal head has been heretofore known. Main printing methods used by such a thermal printer include sublimation method, melting method, and heat-sensitive method. The thermal head is pressed against paper used for printing (such as roll paper) conveyed onto the platen from over the ink ribbon to perform printing. That is, in any printing method, plural heat-generating resistors are arrayed on the thermal head, and the resistors are selectively energized electrically according to gray levels. Printing is performed on the roll paper by making use of thermal energy produced at that time.
For example, in the case of sublimation line type thermal printer, heat-generating resistors are arranged in lines on a thermal head. An ink ribbon and roll paper are conveyed into the space between the thermal head and the platen roller. The head is pressed against the platen roller to hold the ribbon and the paper therebetween. Then, the heat-generating resistors of the thermal head are selectively activated electrically. The inks of the ink ribbon are sublimated by the thermal energy produced at this time and transferred onto the roll paper. Consequently, an image is created.
Generally, the ink ribbon used for such a thermal printer is wound in the space between the supply reel and the take-up reel within a ribbon cassette. Different color inks (e.g., inks of yellow (Y), magenta (M), and cyan (C)) and a transparent laminate ink (L) are successively and repetitively arranged on a base film in a direction perpendicular to the direction in which the ink ribbon is wound off the reel (direction of conveyance). The color inks (Y, M, C) are successively transferred to the roll paper based on information about an image to be printed. Thus, an image is created.
The transparent laminate ink (L) is used to protect the image formed by the color inks (Y, M, C). That is, a totally transparent laminate layer is formed by thermal transfer from over the image made up of the color inks (Y, M, C), thus improving the chemical resistance, solvent resistance, resistance to greases and oils, wear resistance, and other characteristics of the color image. Furthermore, the transparent laminate layer enhances the glossiness of the surface of the formed color image and thus the image quality can be improved.
In this way, the thermal printer forms a color image on the roll paper by the color inks (Y, M, C) and protects the color image by the transparent laminate ink (L). In the stage when the laminate ink (L) is transferred, a matting step for forming a convexo-concave pattern on the surface of the color image may be performed. That is, unevenness created by the matting step can impart desired surface properties such as delustering and net pattern to the color image while retaining the function of the laminate ink (L) for protecting the image.
For example, JP-A-9-272266 (patent reference 1) described below discloses a technique for obtaining arbitrary surface properties by appropriately selecting transfer patterns to form concave portions corresponding to the heating portions of the heat-generating resistors and convex portions corresponding to the non-heating portions when a laminate ink (L) is transferred after a color image is formed on roll paper, so that the surface of the laminate layer is formed into a convexo-concave pattern.
WO 97/39898 (patent reference 2) described below discloses a technique for performing matting processing that produces visually great effects by reading a convexo-concave pattern from a memory when a laminate ink (L) is transferred after a color image is formed on roll paper and forming a net pattern or random convexo-concave pattern by the laminate ink (L).